Mike, if you are talking about restarting the numbering across the whole line as a different thing than restarting individual titles, then yes, DC has only done that twice. But DC has certainly restarted individual titles many other times. Justice League (or JLA) has restarted several times. Also Green Lantern, Hawkman/Hawkgirl, Green Arrow, Flash, etc.
There's a difference between genuinely cancelling a book and then bringing it back at some point in the future with a new #1. I also think it's a different thing if you fundamentally change a book and decide to relaunch it with a new #1, like bringing in Kyle Rayner as GL or bringing back Barry Allen or replacing Cap with Bucky.
However, there have been 6 new #1s for Captain America since 1996. There have been 2 new #1s for Daredevil since 1998. There have been 4 new Iron Man #1s since 1996. There have been 2 new Hulk #1s since 2000. As of next year, there will have been 4 new Avengers #1s since 1996. There have been 3 new Fantastic Four #1s since 1996. Heck, we've even seen two Moon Knight #1s since 2006!
I think DC only has one book that's guilty of constant new #1s, and with Justice League that's usually been accompanied by some kind of creative change to justify it.
I'm not saying DC is innocent of it, merely that they haven't been as guilty of exploiting this sales-boosting tactic as Marvel.